\documentclass[11pt,a4paper]{book}
\usepackage[english,vietnam]{babel}
\usepackage[utf8]{inputenc}

%info
\author{\textbf{Nguyễn Hoàng Nguyện}} 
\title{\textbf{Bài giảng toán rời rạc}}
\date{09/2013}
\begin{document}
\maketitle
\include{Gioithieu}
\include{Chuong1}
\end{document}